pod::usage.3

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arguments. If the verbose level is 2, then the entire manual page is
printed.
.PP
Unless they are explicitly specified, the default values for the exit
status, verbose level, and output stream to use are determined as
follows:
.IP "\(bu" 4
If neither the exit status nor the verbose level is specified, then the
default is to use an exit status of 2 with a verbose level of 0.
.IP "\(bu" 4
If an exit status \fIis\fR specified but the verbose level is \fInot\fR, then the
verbose level will default to 1 if the exit status is less than 2 and
will default to 0 otherwise.
.IP "\(bu" 4
If an exit status is \fInot\fR specified but verbose level \fIis\fR given, then
the exit status will default to 2 if the verbose level is 0 and will
default to 1 otherwise.
.IP "\(bu" 4
If the exit status used is less than 2, then output is printed on
\&\f(CW\*(C`STDOUT\*(C'\fR.  Otherwise output is printed on \f(CW\*(C`STDERR\*(C'\fR.
.PP
Although the above may seem a bit confusing at first, it generally does
\&\*(L"the right thing\*(R" in most situations.  This determination of the default
values to use is based upon the following typical Unix conventions:
.IP "\(bu" 4
An exit status of 0 implies \*(L"success\*(R". For example, \fB\f(BIdiff\fB\|(1)\fR exits
with a status of 0 if the two files have the same contents.
.IP "\(bu" 4
An exit status of 1 implies possibly abnormal, but non-defective, program
termination.  For example, \fB\f(BIgrep\fB\|(1)\fR exits with a status of 1 if
it did \fInot\fR find a matching line for the given regular expression.
.IP "\(bu" 4
An exit status of 2 or more implies a fatal error. For example, \fB\f(BIls\fB\|(1)\fR
exits with a status of 2 if you specify an illegal (unknown) option on
the command line.
.IP "\(bu" 4
Usage messages issued as a result of bad command-line syntax should go
to \f(CW\*(C`STDERR\*(C'\fR.  However, usage messages issued due to an explicit request
to print usage (like specifying \fB\-help\fR on the command line) should go
to \f(CW\*(C`STDOUT\*(C'\fR, just in case the user wants to pipe the output to a pager
(such as \fB\f(BImore\fB\|(1)\fR).
.IP "\(bu" 4
If program usage has been explicitly requested by the user, it is often
desirable to exit with a status of 1 (as opposed to 0) after issuing
the user-requested usage message.  It is also desirable to give a
more verbose description of program usage in this case.
.PP
\&\fBpod2usage\fR doesn't force the above conventions upon you, but it will
use them by default if you don't expressly tell it to do otherwise.  The
ability of \fB\f(BIpod2usage()\fB\fR to accept a single number or a string makes it
convenient to use as an innocent looking error message handling function:
.PP
.Vb 2
\&    use Pod::Usage;
\&    use Getopt::Long;
\&
\&    ## Parse options
\&    GetOptions("help", "man", "flag1")  ||  pod2usage(2);
\&    pod2usage(1)  if ($opt_help);
\&    pod2usage(\-verbose => 2)  if ($opt_man);
\&
\&    ## Check for too many filenames
\&    pod2usage("$0: Too many files given.\en")  if (@ARGV > 1);
.Ve
.PP
Some user's however may feel that the above \*(L"economy of expression\*(R" is
not particularly readable nor consistent and may instead choose to do
something more like the following:
.PP
.Vb 2
\&    use Pod::Usage;
\&    use Getopt::Long;
\&
\&    ## Parse options
\&    GetOptions("help", "man", "flag1")  ||  pod2usage(\-verbose => 0);
\&    pod2usage(\-verbose => 1)  if ($opt_help);
\&    pod2usage(\-verbose => 2)  if ($opt_man);
\&
\&    ## Check for too many filenames
\&    pod2usage(\-verbose => 2, \-message => "$0: Too many files given.\en")
\&        if (@ARGV > 1);
.Ve
.PP
As with all things in Perl, \fIthere's more than one way to do it\fR, and
\&\fB\f(BIpod2usage()\fB\fR adheres to this philosophy.  If you are interested in
seeing a number of different ways to invoke \fBpod2usage\fR (although by no
means exhaustive), please refer to \*(L"\s-1EXAMPLES\s0\*(R".
.SH "EXAMPLES"
.IX Header "EXAMPLES"
Each of the following invocations of \f(CW\*(C`pod2usage()\*(C'\fR will print just the
\&\*(L"\s-1SYNOPSIS\s0\*(R" section to \f(CW\*(C`STDERR\*(C'\fR and will exit with a status of 2:
.PP
.Vb 1
\&    pod2usage();
\&
\&    pod2usage(2);
\&
\&    pod2usage(\-verbose => 0);
\&
\&    pod2usage(\-exitval => 2);
\&
\&    pod2usage({\-exitval => 2, \-output => \e*STDERR});
\&
\&    pod2usage({\-verbose => 0, \-output  => \e*STDERR});
\&
\&    pod2usage(\-exitval => 2, \-verbose => 0);
\&
\&    pod2usage(\-exitval => 2, \-verbose => 0, \-output => \e*STDERR);
.Ve
.PP
Each of the following invocations of \f(CW\*(C`pod2usage()\*(C'\fR will print a message
of \*(L"Syntax error.\*(R" (followed by a newline) to \f(CW\*(C`STDERR\*(C'\fR, immediately
followed by just the \*(L"\s-1SYNOPSIS\s0\*(R" section (also printed to \f(CW\*(C`STDERR\*(C'\fR) and
will exit with a status of 2:
.PP
.Vb 1
\&    pod2usage("Syntax error.");
\&
\&    pod2usage(\-message => "Syntax error.", \-verbose => 0);
\&
\&    pod2usage(\-msg  => "Syntax error.", \-exitval => 2);
\&
\&    pod2usage({\-msg => "Syntax error.", \-exitval => 2, \-output => \e*STDERR});
\&
\&    pod2usage({\-msg => "Syntax error.", \-verbose => 0, \-output => \e*STDERR});
\&
\&    pod2usage(\-msg  => "Syntax error.", \-exitval => 2, \-verbose => 0);
\&
\&    pod2usage(\-message => "Syntax error.",
\&              \-exitval => 2,
\&              \-verbose => 0,
\&              \-output  => \e*STDERR);
.Ve
.PP
Each of the following invocations of \f(CW\*(C`pod2usage()\*(C'\fR will print the
\&\*(L"\s-1SYNOPSIS\s0\*(R" section and any \*(L"\s-1OPTIONS\s0\*(R" and/or \*(L"\s-1ARGUMENTS\s0\*(R" sections to
\&\f(CW\*(C`STDOUT\*(C'\fR and will exit with a status of 1:
.PP
.Vb 1
\&    pod2usage(1);
\&
\&    pod2usage(\-verbose => 1);
\&
\&    pod2usage(\-exitval => 1);
\&
\&    pod2usage({\-exitval => 1, \-output => \e*STDOUT});
\&
\&    pod2usage({\-verbose => 1, \-output => \e*STDOUT});
\&
\&    pod2usage(\-exitval => 1, \-verbose => 1);
\&
\&    pod2usage(\-exitval => 1, \-verbose => 1, \-output => \e*STDOUT});
.Ve
.PP
Each of the following invocations of \f(CW\*(C`pod2usage()\*(C'\fR will print the
entire manual page to \f(CW\*(C`STDOUT\*(C'\fR and will exit with a status of 1:
.PP
.Vb 1
\&    pod2usage(\-verbose  => 2);
\&
\&    pod2usage({\-verbose => 2, \-output => \e*STDOUT});
\&
\&    pod2usage(\-exitval  => 1, \-verbose => 2);
\&
\&    pod2usage({\-exitval => 1, \-verbose => 2, \-output => \e*STDOUT});
.Ve
.Sh "Recommended Use"
.IX Subsection "Recommended Use"
Most scripts should print some type of usage message to \f(CW\*(C`STDERR\*(C'\fR when a
command line syntax error is detected. They should also provide an
option (usually \f(CW\*(C`\-H\*(C'\fR or \f(CW\*(C`\-help\*(C'\fR) to print a (possibly more verbose)
usage message to \f(CW\*(C`STDOUT\*(C'\fR. Some scripts may even wish to go so far as to
provide a means of printing their complete documentation to \f(CW\*(C`STDOUT\*(C'\fR
(perhaps by allowing a \f(CW\*(C`\-man\*(C'\fR option). The following complete example
uses \fBPod::Usage\fR in combination with \fBGetopt::Long\fR to do all of these
things:
.PP
.Vb 2
\&    use Getopt::Long;
\&    use Pod::Usage;
\&
\&    my $man = 0;
\&    my $help = 0;
\&    ## Parse options and print usage if there is a syntax error,
\&    ## or if usage was explicitly requested.
\&    GetOptions(\*(Aqhelp|?\*(Aq => \e$help, man => \e$man) or pod2usage(2);
\&    pod2usage(1) if $help;
\&    pod2usage(\-verbose => 2) if $man;
\&
\&    ## If no arguments were given, then allow STDIN to be used only
\&    ## if it\*(Aqs not connected to a terminal (otherwise print usage)
\&    pod2usage("$0: No files given.")  if ((@ARGV == 0) && (\-t STDIN));
\&    _\|_END_\|_
\&
\&    =head1 NAME
\&
\&    sample \- Using GetOpt::Long and Pod::Usage
\&
\&    =head1 SYNOPSIS
\&
\&    sample [options] [file ...]
\&
\&     Options:
\&       \-help            brief help message
\&       \-man             full documentation
\&
\&    =head1 OPTIONS
\&
\&    =over 8
\&
\&    =item B<\-help>
\&
\&    Print a brief help message and exits.
\&
\&    =item B<\-man>
\&
\&    Prints the manual page and exits.
\&
\&    =back
\&
\&    =head1 DESCRIPTION
\&
\&    B<This program> will read the given input file(s) and do something
\&    useful with the contents thereof.
\&
\&    =cut
.Ve
.SH "CAVEATS"
.IX Header "CAVEATS"
By default, \fB\f(BIpod2usage()\fB\fR will use \f(CW$0\fR as the path to the pod input
file.  Unfortunately, not all systems on which Perl runs will set \f(CW$0\fR
properly (although if \f(CW$0\fR isn't found, \fB\f(BIpod2usage()\fB\fR will search
\&\f(CW$ENV{PATH}\fR or else the list specified by the \f(CW\*(C`\-pathlist\*(C'\fR option).
If this is the case for your system, you may need to explicitly specify
the path to the pod docs for the invoking script using something
similar to the following:
.PP
.Vb 1
\&    pod2usage(\-exitval => 2, \-input => "/path/to/your/pod/docs");
.Ve
.PP
In the pathological case that a script is called via a relative path
\&\fIand\fR the script itself changes the current working directory
(see \*(L"chdir\*(R" in perlfunc) \fIbefore\fR calling pod2usage, Pod::Usage will
fail even on robust platforms. Don't do that.
.SH "AUTHOR"
.IX Header "AUTHOR"
Please report bugs using <http://rt.cpan.org>.
.PP
Brad Appleton <[e-mail]>
.PP
Based on code for \fB\f(BIPod::Text::pod2text()\fB\fR written by
Tom Christiansen <[e-mail]>
.SH "ACKNOWLEDGMENTS"
.IX Header "ACKNOWLEDGMENTS"
Steven McDougall <[e-mail]> for his help and patience
with re-writing this manpage.